Method of electric-arc welding of tubular products with magnetic control of the arc

ABSTRACT

A method for the electric-arc welding of tubular products, in which a magnetic field is made to act upon the arc so as to control the process of welding, the method characterized in that the magnetic field is established in the welding zone by passing an electric current along the workpiece from a separate current source.

United States Patent 1191 Raichuk et 'al.

1451 Jan.9, 1973 l 54] METHOD OF ELECTRIC-ARC WELDING OF TUBULARPRODUCTS WITH MAGNETIC CONTROL OF THE ARC Inventors: Jury IsnkovichRaichuk, prospekt Filed:

June 28, 1971 Appl. No.: 157,260

us; (:1. ..219/6l, 219/62, 219/123 1111.01. ..B23k 31/06 Field of Search..219/60, 61, 62, 12 3, 124, 12s

[56] References Cited UNITED STATES PATENTS 1,827,657 10/1931 lpsen..2l9/l23 Primary Examiner-J. V. Truhe Assistant Examiner-L. A.Schutzman Attorney-Holman & Stern [57] ABSTRACT A method for theelectric-arc welding of tubular products, in which a magnetic field ismade to act upon the arc so as to control the process of welding,

the method characterized in that the magnetic field is established inthe welding zone by passing an electric current along the workpiece froma separate current source.

3 C 2 D w F u e METHOD OF ELECTRIC-ARC WELDING OF TUBULAR PRODUCTS WITHMAGNETIC CONTROL OF THE ARC The present invention relates tometal-working industries, and more specifically to electric-arc weldingof tubular products and may be utilized in the fabrication ofelectric-welded straightand spiral-seam pipes and tubes.

Widely known in the prior art is a method for the electric-arc weldingof tubular products which consists in that the workpiece is set up in awelding machine, an electrode is brought into the welding zone, and amagnetic field is established near the welding zone and at right anglesto the edges to be welded. After that, the work-piece and electrode areconnected to a welding source, a welding arc is initiated between theelectrode and workpiece, and the two are made to move relative to eachother and along the edge to be welded.

The magnetic field in the above-mentioned method can be established byone or several electromagnets each consisting of a coil and a core, withpoles placed near the welding arc.

The heat generated in the welding zone produces a region of molten metalwhich, on cooling, produces a solidified weld.

An increase in welding speed without any controlling action ofthemagnetic field on the arc would result in a poor shape and quality ofthe weld, such as a narrow bead, undercuts, lack of proper fusion, andother flaws.

The transverse magnetic field causes the arc to deflect one way or theother, thereby controling the progress of welding. The effect isespecially Wholesome when the arc is deflected in the direction ofwelding. This deflection of the arc improves the quality of the weld andenables the welding speed to be raised. Conversely, the transversemagnetic field may be made to change the form of the weld while keepingthe welding speed unchanged.

The above-mentioned method is widely used in the welding of non-magneticsteels and alloys. The application of this method to the welding offerromagnetic materials entails a number of difficulties, and theselimit its field of use.

These difficulties consist in that the ferromagnetic material of theworkpiece provides a bypass for the magnetic field influencing the are,thereby reducing its intensity within the arc zone and its effect on thearc.

Because of this, the power of the electromagnets has to be increasedconsiderably.

The extent to which the magnetic flux is bypassed around the arc dependson the size of the air gaps between the poles of the electromagnet andthe edges of the ferromagnetic workpiece. Poor fit-up or other likecauses or a pipe skelp or burr may increase or decrease the gap betweenthe edges of the workpiece. These variations in said air-gaps may resultin instability of the magnetic flux in the arc zone, thereby seriouslyimpairing the effectiveness of magnetic are control.

The main object of the present invention is to provide a method for thewelding of tubular products with a magnetically controlled electric arc,such that workpieces made of magnetically permeable materials can besuccessfully welded, irrespective of the position of the welding edgesin space. i

Another object of the present invention is to improve the shape andquality of welds at a constant welding speed or alternatively to raisethe welding speed with a good quality of welds.

These effects are obtained owing to the deformation of the welding areby a magnetic field and the utilization of the forces applied to themolten metal of the welding bath as a result of interaction between thetransverse magnetic field and the current flowing in the molten metal ofthe weld region.

With these and other objects in view, the present invention resides in amethod of electric-arc welding of tubular products comprising arranginga workpiece in a welding machine, advance of an electrode into thewelding zone, establishment ofa magnetic field around the welding zone,connection of the workpiece and electrode to a welding source,initiation of a welding are between the electrode and workpiece, andsubsequent displacement of the electrode and workpiece relative to eachother, the method of the invention characterized in that the magneticfield around the welding zone is established by allowing a current fromanother source to flow along the workpiece.

To improve the effectiveness of arc control and to prevent this currentfrom being by passed through the bedframe of the welding machine, thetubular workpiece should preferably be electrically insulated from thewelding machine on at least one side from the plane which is normal tothe longitudinal axis of the workpiece and in which the electric arcoccurs.

The method of the invention functions in the following manner.

The current allowed to flow along the workpiece in the course of weldingestablishes a transverse magnetic field in the arc zone, acting on boththe arc and the bath or region of molten metal.

While in the prior-art method the unheated part of the closed magneticcircuit formed by the ferromagnetic tubular workpiece serves as amagnetic shunt reducing the strength of the magnetic field in thewelding zone, in the method disclosed herein this part of the workpieceis utilized as a magnetic circuit building up the total magnetic fieldin the arc zone.

Any change in the relative position of the work edges in this case hasno effect on the magnitude of the current applied to the workpiece froman additional source and, as a consequence, on the strength of themagnetic field in the welding zone. As a result, the controlling effectof the magnetic field on the progress of welding is stabilized and madeindependent of the relative position of the work edges in the course ofwelding.

With the current flowing along the workpiece so that the arc isdeflected in the direction of welding and because of the stability ofthe controlling magnetic field, the quality of the welds issubstantially improved and the welding speed may also be considerablyraised.

Besides, part of the current passed along the workpiece has its path inthe molten metal of the welding pool. Interaction of this part ofcurrent with the transverse magnetic field due to both the weldingcurrent and the current passed through the workpiece changes the shapeof the welding pool, which further serves to improve the formation ofthe weld. The current passed through the workpiece from an additionalsource may be direct, alternating, pulsating, or combined.

The invention will be more fully understood from the followingdescription of a preferred embodiment of a method for the electric arcwelding of spiral-seam pipes, when read in connection with theaccompanying drawings wherein:

, FIG. 1 is a top view of an apparatus for the fabrication ofspiral-seam pipes a from a steel strip, according to the invention;

FIG. 2 shows section along line ll-ll of FIG. 1.

Referring to FIG. 1, in the fabrication of spiral-seam pipes, anelongated steel strip 1 is folded by a shaping device (not shown in thedrawing) of a pipe-welding machine 2 into a spiral to form a pipe 3 (thedirection in which the skelp is advanced is shown by the arrow A), andthe pipe thus formed is welded from the inside and outside.

An electrode 5 is advanced by a welding head 4 to a point B where theedges of the strip 1 and of the formed pipe 3 converge.

In the welding zone of the inside weld a magnetic field is establishedby the current passed along the pipe 3 from a source 6 connected to thepipe via members 7 and 8. ln the case of submerged arc welding, therequisite blanket of flux is built up by feeding the latter into thewelding zone by a flux-feeding device 9.

In order to make the inside weld, the electrode 5 and the tube 3 areconnected to the welding source 10 via the welding head 4 and thecurrent transmitting member 7.

A welding arc is initiated between the electrode 5 and the edges of theworkpiece and, as a result of continuous advance of the steel skelp 1into the welding zone, a pipe is formed and its inside weld is made.

To enhance the effectiveness of the magnetic control of welding with theaid of the current passed along the workpiece, the pipe 3 iselectrically insulated from the bedframe of the welding machine 2insulating spacers l l.

Magnetic control by current in the welding of the inside weld consistsin deflecting the arc in the direction of welding and in reducing theoutflow of molten metal from the welding puddle owing the action ofmagnetohydrodynamic forces on the molten metal.

This is achieved by the proper selection of the relative polarity forthe sources 10 and 6. The polarity for connection of the auxiliarysource 6 is shown in the accompanying diagram where the electrode 5 isconnected to the positive side of the source 10. In this case, thecurrent flowing in the workpiece from the source 6 deflects the arc inthe direction of welding. Besides, there are forces acting on the moltenmetal of the weld puddle, which, owing to the polarities of the sources6 and 10 as shown, are directed upwards, towards the axis of the pipe sothat they prevent the molten metal from running out of the weldingpuddle. This improves the quality of the weld and serves to increase thespeed of welding.

The outside weld of this pipe is made from above, at a distance frompoint B equal to 1% turns of the weld, with a welding head 12 and anelectrode 13 connected to a welding source 14 one side of which isconnected to the pipe being welded via a current supplying member 15,and the other side to the welding head 12.

The accompanying diagram does not show the magn etic control of the aremaking the outside weld of the pipe. lf necessary, this may eaccomplished In the same way as in the case of the inside weld.

In the example on hand, magnetic control is applied to the are makingthe inside weld which is especially difficult to shape properly.

The point is that with a certain increase in the welding speed theproper shaping of the outside weld may be accomplished by shifting thewelding point along the edges against the direction of travel, while inthe case of the inside weld there is no such possibility.

The method for the electric-arc welding of pipes disclosed herein offersa means for a substantial increase in the speed of welding ofspiral-seam pipes of mangeti cally permeable material.

What is claimed is l. A method for the production of a tubular productby electric-arc welding of a workpiece, comprising the followingoperations: placing of the workpiece in a welding machine in a weldingzone thereof; advancing an electrode to the welding zone; connectingsaid workpiece through a current inlet contact member and a currentoutlet contact member away from said electrode to a first source ofcurrent and passing a current through the workpiece in the direction ofthe weld seam to be formed to establish a magnetic field in saidworkpiece; connecting the workpiece and said electrode to a secondcurrent source which is the welding source; initiating an are betweenthe electrode and workpiece causing molten metal at the region of saidare; and subsequently displacing the electrode and workpiece relative toeach other, whereby said current from said first source flows throughsaid molten metal, and the current carrying molten metal under theinfluence of said magnetic field results in production of a sound weld.

2. A method of claim 1, which includes the step of providing electricalinsulation of the tubular workpiece from the welding machine on at leastone side from a plane which is normal to the longitudinal axis of theworkpiece and in which the welding arc is maintained.

3. A method for the production of a tubular product by electric arcwelding of a workpiece, comprising the following operations: placing theworkpiece in a welding machine in a welding zone thereof; providingelectrical insulation of said workpiece from the welding machine body;advancing a welding electrode to the welding zone; connecting saidworkpiece to a first source of current and passing a current through theworkpiece to establish a magnetic field in said workpiece; connectingthe workpiece and said welding electrode to a welding current zone;passing current to the welding electrode and initiating an arc betweenthe welding electrode and said workpiece; and displacing said weldingelectrode and said workpiece relative to each other.

1. A method for the production of a tubular product by electricarcwelding of a workpiece, comprising the following operations: placing ofthe workpiece in a welding machine in a welding zone thereof; advancingan electrode to the welding zone; connecting said workpiece through acurrent inlet contact member and a current outlet contact member awayfrom said electrode to a first source of current and passing a currentthrough the workpiece in the direcTion of the weld seam to be formed toestablish a magnetic field in said workpiece; connecting the workpieceand said electrode to a second current source which is the weldingsource; initiating an arc between the electrode and workpiece causingmolten metal at the region of said arc; and subsequently displacing theelectrode and workpiece relative to each other, whereby said currentfrom said first source flows through said molten metal, and the currentcarrying molten metal under the influence of said magnetic field resultsin production of a sound weld.
 2. A method of claim 1, which includesthe step of providing electrical insulation of the tubular workpiecefrom the welding machine on at least one side from a plane which isnormal to the longitudinal axis of the workpiece and in which thewelding arc is maintained.
 3. A method for the production of a tubularproduct by electric arc welding of a workpiece, comprising the followingoperations: placing the workpiece in a welding machine in a welding zonethereof; providing electrical insulation of said workpiece from thewelding machine body; advancing a welding electrode to the welding zone;connecting said workpiece to a first source of current and passing acurrent through the workpiece to establish a magnetic field in saidworkpiece; connecting the workpiece and said welding electrode to awelding current zone; passing current to the welding electrode andinitiating an arc between the welding electrode and said workpiece; anddisplacing said welding electrode and said workpiece relative to eachother.